In manufactured articles, such as automobiles, household appliances and industrial machines, a metal and a resin often need to be firmly bonded together. In conventional methods, an adhesive is used at normal temperature or under heating to integrally bond a metal and a synthetic resin. Alternatively, an engineering resin with high strength may be bonded to a magnesium alloy, an aluminum alloy, or ferroalloys such as stainless steel without an adhesive.
Nano molding technology (NMT) is a technique of integrally bonding a metal and a resin, which allows the resin to be directly injection molded on a surface of a metal sheet by nano molding the surface of the metal sheet so as to obtain a metal-resin integrally molded product. For effective bonding of a metal and a resin, NMT may replace commonly used insert molding or zinc-aluminum or magnesium-aluminum die casting so as to provide a metal-resin integrally molded product with low cost and high performance. Compared with other bonding technology, NMT may reduce the weight of the final product, ensure excellent strength of the mechanical structure, high processing rate, high output, and allow more appearance decoration methods, thereby applicable to vehicles, IT equipment, and 3C products.
Japan's Taisei Plas Co., Ltd. filed a series of patent applications including, for example, CN1492804A, CN1717323A, CN101341023A and CN101631671A, which disclose a method for integrally molding a metal and a resin composition. For example, by using a resin composition containing polyphenylene sulfide (PPS), polybutylene terephthalate (PBT) and polyamide (PA) with high crystallinity as an injection molding material, the resin composition is directly injection molded on a surface of a nano molded aluminum alloy layer to allow the resin composition to immerse in a nanoscale micropore, so as to obtain a metal-resin integrally molded product with a certain mechanical strength. However, because the resins used in this method are all highly crystalline resins, on one hand, long cooling time and strict mould temperature are required during the molding to ensure the mechanical performance of the product, and annealing is also required to ensure the dimensional stability; on the other hand, highly crystalline resins cause the surface of the plastic layer difficult to process, and consequently cause large appearance difference between the plastic layer and the metal sheet when the plastic layer is subsequently used in an appearance article, which is not suitable for the surface decoration of a plastic article. Moreover, the metal-resin integrally molded product produced by this method has insufficient toughness when used in electronic apparatus components, and consequently the structure of the metal-resin integrally molded product is difficult to design.